K327 / K328 / 2027

Lesson 3 of 7 / Nutrition in humans

Absorption, assimilation and the liver

What happens to glucose after it enters the blood?

I can trace absorbed nutrients through the hepatic portal vein and explain assimilation.

  • I can describe named digestive organs and ingestion, digestion, absorption, assimilation and egestion.Syllabus

    Syllabus K327 / K328, Topic 4(a). Describe named digestive organs and ingestion, digestion, absorption, assimilation and egestion.

  • I can state the hepatic portal vein function.Syllabus

    Syllabus K327 / K328, Topic 4(c). State the hepatic portal vein function.

  • I can state the five specified liver roles.Syllabus

    Syllabus K327 / K328, Topic 4(d). State the five specified liver roles.

About 5 min

Make a guess. You are not marked.

Glucose has just been absorbed from your small intestine into the blood. Where does that blood go first?

  1. Straight to the heart, then to all cells.
  2. To the kidneys, to be filtered.
  3. To the liver, in the hepatic portal vein.
  4. To the muscles, which need it most.
Show the answer

To the liver, in the hepatic portal vein.

The hepatic portal vein takes nutrient-rich blood straight to the liver, which processes it before it goes on.

The key idea

The hepatic portal vein carries nutrient-rich blood from the small intestine to the liver. The liver processes nutrients before blood carries them onwards.

Hepatic means related to the liver. Follow glucose and amino acids in blood from the intestine; do not confuse this vessel with the duct that carries bile.

Explore the idea

Follow absorbed glucose to the liver

Hepatic portal route and glucose storageBlood flows from small intestine capillaries through the hepatic portal vein to the liver. Liver cells convert some glucose to glycogen.Small intestineblood capillariesHepaticportal veinLiverGlucoseGlycogenBlood carries nutrientsonwards

The hepatic portal vein delivers nutrient-rich blood to the liver. Converting absorbed glucose into glycogen is assimilation and storage.

Original flow diagram. Hormonal regulation is studied in homeostasis. Absorbed fat follows mainly the lacteal and lymph route, not this immediate portal route.

Explanation

Digestion produces small soluble molecules that can cross the wall of the small intestine. This crossing is absorption. Glucose and amino acids enter the blood, which carries them away from the absorption surface.

The hepatic portal vein carries blood rich in absorbed nutrients from the small intestine to the liver. It is a blood vessel, not a bile duct. Bile moves from the liver towards the intestine through ducts, so these routes carry different materials in different directions.

Liver cells can remove some glucose and convert it into glycogen for storage. When needed, glycogen can be broken down to glucose and glucose can be released into blood. Glucose is a small sugar; glycogen is a much larger storage molecule made from glucose units.

Assimilation is the use or incorporation of absorbed nutrients by cells. Glucose can be used in respiration, and amino acids can form proteins for growth and repair. Absorption describes entering the transport system from the intestine; assimilation describes what cells subsequently do with the nutrients.

Step by step
  1. 1

    Absorb

    Small soluble nutrients cross the intestinal wall into blood.

  2. 2

    Transport

    The hepatic portal vein takes nutrient-rich blood to the liver.

  3. 3

    Assimilate

    Cells use nutrients, for example by building proteins or storing glucose as glycogen.

Worked example

After a carbohydrate-rich meal

Glucose concentration rises in blood leaving the small intestine. Name the vessel taking it to the liver and describe one way the liver can store it.

One way to explain it

The hepatic portal vein takes the glucose-rich blood to the liver. Liver cells convert glucose into glycogen for storage. Glycogen can later be broken down to glucose when needed.

Why this answer works
  • Give the precise vessel name.
  • Use the correct direction: intestine to liver.
  • Distinguish glucose from its storage molecule glycogen.

Watch out for this

A student says: "The hepatic portal vein carries bile from the liver to the intestine." What is wrong with this?

Show the answer

It carries blood from the intestine to the liver. Bile travels towards the intestine through bile ducts, which are not blood vessels.

Check your understanding

Which route and process are correctly paired?

  1. Assimilation: removal of undigested food through the anus.
  2. Bile duct: glucose-rich blood from the intestine to the liver.
  3. Hepatic portal vein: nutrient-rich blood from the small intestine to the liver.
Show the answer

Hepatic portal vein: nutrient-rich blood from the small intestine to the liver.

Glucose can then be assimilated, for example by conversion to glycogen in liver cells.

Quick recall

Card 1 of 3. Answer in your head, then check.

What happens to glucose after it enters the blood?

You can return to this lesson any time.